Tool holder

ABSTRACT

In a shank portion of an end mill which is chucked by a tool holder, flat surfaces are formed at a plurality of circumferential positions in the outer periphery of the shank portion so that the flat surfaces abut on side lock bolts attached to a body of the tool holder.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. patent application Ser. No.13/657,921 filed on Oct. 23, 2012, the entire disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to shank portions of end mills amongcutters such as end mills and reamers, and tool holders that chuck theshank portion of the end mill.

2. Background Art

Conventionally, shank portions of cutters such as end mills and reamers,and tool holders that chuck the shank portion of the cutter are proposedin, e.g., Japanese Unexamined Patent Publication Nos. 2002-346864 and2001-87969 and Japanese Utility Model Publication No. H06-80509. Suchconventional tool holders include two side lock bolts. The shank portionof the cutter basically has a circular cross section, and two flatsurfaces are formed in the outer periphery of the shank portion. Byfastening the two side lock bolts, the tip ends of the side lock boltsabut on the flat surfaces, respectively, whereby the shank portion ofthe cutter is chucked.

SUMMARY OF INVENTION

The inventors found that there is still room for improvement in theshank portions of the conventional cutters. Since the two flat surfacesare provided at a predetermined circumferential position on the outerperiphery of the shank portion so as to be aligned with each other, theshank portion is subjected to a specific radial pressing force from theside lock bolts. Since the shank portion is pressed in the specificradial direction by the side lock bolts, there is still room forimprovement in chucking. Moreover, displacement of the axis may occur.Specifically, the axis of the shank portion may be displaced from aproper position.

In view of the above problems, it is an object of the present inventionto provide a chucking structure improved over the conventionalstructures.

In order to achieve the above object, a shank structure of an end millaccording to a first invention includes a shank portion that is chuckedby a tool holder, wherein first and second flat surfaces are formed atdifferent circumferential positions on an outer periphery of the shankportion so that the first and second flat surfaces abut on side lockbolts attached to a body of the tool holder.

According to the first embodiment, since the flat surfaces are formed atthe different circumferential positions in the shank portion, the shankportion is subjected to a plurality of radial pressing forces fromdifferent directions from each other. Thus, the shank portion is notsubjected to a specific radial pressing force from the side lock bolts,and a side lock bolt chucking mechanism improved over the conventionalstructures can be provided. The first invention does not excludeformation of an additional flat surface at a different circumferentialposition in addition to the first and second flat surfaces.

In a preferred embodiment of the first invention, at least one of thefirst and second flat surfaces is a surface tilted at a predeterminedangle in a range of 1 to 10 degrees, both inclusive, with respect to anaxis of the shank portion so as to face toward a tip end of the endmill. According to this embodiment, the pressing force that is appliedfrom the side lock bolt to the flat surface of the shank portionincludes a component toward an axial rear end, and biases the shankportion so as to insert the shank portion into the tool holder. Thus,the shank portion can be more reliably chucked. In a more preferredembodiment, the flat surface is a surface tilted at 5 degrees withrespect to the axis of the shank portion so as to face toward the tipend of the end mill.

If the first and second flat surfaces are tilted at an angle of lessthan 1 degree with respect to the axis of the shank portion, the forcethat biases the shank portion so as to insert the shank portion into thetool holder is reduced. If the first and second flat surfaces are tiltedat an angle of more than 10 degree with respect to the axis of the shankportion, the force that presses the shank portion in the radialdirection is reduced. In another embodiment, the flat surface of theshank portion may be parallel to the axis.

As a preferred embodiment of the first invention, the first flat surfaceis provided at a position of a predetermined angle in a range of 60 to120 degrees, both inclusive, about an axis of the shank portion withrespect to the second flat surface. According to this embodiment, thepressing force is applied to the first flat surface in a directioncrossing the direction in which the pressing force is applied to thesecond flat surface. Thus, the shank portion is pressed in a preferablemanner against the inner peripheral surface of the tool holder, andchucking is improved. In a more preferred embodiment, the first flatsurface is provided at a position of a predetermined angle in a range of80 to 100 degrees, both inclusive, about the axis of the shank portionwith respect to the second flat surface. In a more preferred embodiment,the first flat surface is provided at a position of 90 degrees about theaxis of the shank portion with respect to the second flat surface.

If the angle between the first flat surface and the second flat surfaceis less than 60 degrees, the force that presses the shank portion in thespecific radial direction is increased. If the angle between the firstflat surface and the second flat surface is more than 120 degrees, therate at which the total force of the force that is applied from the sidelock bolt to the first flat surface and the force that is applied fromthe side lock bolt to the second flat surface is cancelled is increased,and the force that presses the shank portion in the radial directiontoward the tool holder is reduced.

In a preferred embodiment, at least one of the first and second flatsurfaces is surface-treated so as to have a higher friction coefficient.According to this embodiment, the side lock bolt is less likely to slideon the surface-treated flat surface when the surface-treated flatsurface abuts on the side lock bolt. Thus, the side lock bolt canreliably press the flat surface. This makes it more difficult for theshank portion to come off from the tool holder. Examples of this surfacetreatment include a shot peening process and a plating process.Alternatively, other physical or chemical treatment may be performed.

In an embodiment of the first invention, the shank structure of the endmill further includes a fluid passage extending from the shank portiontoward a tip end of the end mill. According to this embodiment, liquidsuch as cutting fluid or cleaning fluid can be supplied from the toolholder to the end mill, and the liquid can be directly injected from acutting edge of the end mill onto a workpiece. In another embodiment,the liquid may be injected from the tool holder toward the cutting edgewithout flowing through the end mill.

A tool holder according to a second invention includes: a cylindricaltool attaching/detaching portion having in its center a tool holdinghole extending from an axial tip end toward an axial rear end; and firstand second side lock bolts that are respectively screwed in first andsecond through holes formed at different circumferential positions so asto extend from an outer peripheral surface of the toolattaching/detaching portion to an inner peripheral surface thereof,wherein a shank portion of an end mill is chucked by fastening androtating the first and second side lock bolts so that flat tip end facesformed at tip ends of the first and second side lock bolts abut on theshank portion of the end mill. According to the second invention, theflat tip end faces at the tip ends of the first and second side lockbolts face the first and second flat surfaces formed in the shankportion, and the shank structure of the first invention can be chuckedin a preferable manner. The second invention does not exclude formationof an additional side lock bolt at a different circumferential positionin addition to the first and second side lock bolts.

In a preferred embodiment, the tool attaching/detaching portion furtherhas a centering holding unit that is provided in the axial tip end ofthe tool attaching/detaching portion to center and hold the shankportion of the end mill, and the first and second side lock bolts chuckthe shank portion of the end mill with the shank portion of the end millbeing centered and held by the centering holding unit.

According to this embodiment, since the shank portion of the end mill iscentered, the tip end of the tool attaching/detaching portion can holdthe shank portion of the end mill uniformly in the circumferentialdirection. Thus, the axis of the tool holder is aligned with the axis ofthe end mill, and the end mill can be held with high accuracy. Then, theplurality of side lock bolts perform a function to provide finalfastening, and thus prevent rotation of the shank portion of the endmill. Since the centering holding unit and the plurality of side lockbolts are provided, chucking is not loosened even if a cutting processis performed for a long time.

The centering holding unit is not specifically limited. In anembodiment, the centering holding unit includes a taper that is formedin the outer peripheral surface of the tool attaching/detaching portionso as to be tapered toward the axial tip end, a cylindrical fasteningmember that has an inner peripheral surface tapered at a same angle asthe outer peripheral surface of the tool attaching/detaching portion andsurrounds the outer peripheral surface of the tool attaching/detachingportion which is located closer to the axial tip end than the side lockbolts, a plurality of needle rollers that are placed in an annular spacebetween the inner peripheral surface of the fastening member and theouter peripheral surface of the tool attaching/detaching portion, and aretainer that holds the needle rollers so that the needle rollers aretilted at a predetermined angle in a circumferential direction withrespect to an axis of the tool attaching/detaching portion, and thefastening member is rotated so that the needle rollers revolve in ahelical pattern while rotating, whereby the tool holding hole is reducedin diameter or is restored.

In this embodiment, the fastening member is rotated in a fasteningdirection, and the tool holding hole is reduced in diameter along apredetermined axial dimension of the tool holding hole due to thetapering action. Thus, the axis of the tool holder is aligned with theaxis of the end mill, and the shank portion can be fastened and heldwith a force that is uniform along the entire circumference of the shankportion. Accordingly, the centering holding unit can be implemented in apreferable manner. In another embodiment, the centering holding unit maybe a taper collet chuck for centering, a shrink-fit chuck for centering,a hydro chuck for centering, or CoroGrip (registered trademark) forcentering.

In an embodiment, the side lock bolt includes a bolt body that isscrewed in the through hole, and a pressing member having a pressingsurface that abuts on the shank portion of the end mill, and beingattached to a tip end of the bolt body so that orientation of thepressing surface can be changed as desired. In this embodiment, even ifthe flat surface of the shank portion does not extend in a directionthat crosses a direction in which the side lock bolt advances, thepressing surface at the tip end of the side lock bolt changes itsorientation according to the flat surface of the shank portion andsurface contacts the flat surface when the side lock bolt is rotated inthe fastening direction. Accordingly, the side lock bolt firmly pressesthe flat surface of the shank portion, and the shank portion can be morereliably chucked.

In a preferred embodiment, the flat tip end face of the side lock boltmay be surface-treated so as to have a higher friction coefficient. Inthis embodiment, the surface-treated tip end face of the side lock boltis less likely to slide on the flat surface of the shank portion whenthe surface-treated tip end abuts on the flat surface of the shankportion. Thus, the side lock bolt can reliably press the flat surface.This makes it more difficult for the shank portion to come off from thetool holder. Examples of this surface treatment include a shot peeningprocess and a plating process. Alternatively, other physical or chemicaltreatment may be performed. The side lock bolt that is surface-treatedso as to have a higher friction coefficient is at least one of the firstand second side lock bolts. The flat surface of the shank portion whichabuts on the tip end face of this side lock bolt is at least one of thefirst and second flat surfaces.

In a further preferred embodiment, the tool holder may comprise astopper member provided on a bottom side of the tool holding hole andadapted to define an axial position of the shank portion of the end millinserted in the tool holding hole.

In a much further preferred embodiment, the stopper member may have acommunication passage extending through the stopper member in the axialdirection, and an opening at the tip end of the communication passage isconfigured to connect to an opening at the rear end of a fluid passageof the shank portion of the end mill.

Thus, in the shank structure of the present invention, the shank portionof the end mill is not subjected to the specific radial force, andimproved chucking is provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view showing an end mill according to an embodiment ofthe present invention.

FIG. 2 is an overall view showing an end mill and a tool holderaccording to an embodiment of the present invention.

FIG. 3 is a transverse sectional view taken along line III-III in FIG.2.

FIG. 4 is a front view showing an axial tip end of a tool holder.

FIG. 5 is a front view showing an axial tip end of a tool holder havinga lid member removed therefrom.

FIG. 6 is an overall view showing a groove formed in an inner peripheralsurface of a tool attaching/detaching portion of a tool holder.

FIG. 7 is an overall view showing a tool holder before chucking, whichis not holding a shank portion of an end mill.

FIG. 8 is a side view showing an end mill according to anotherembodiment of the present invention.

FIG. 9 is an overall view showing a tool holder according to anotherembodiment of the present invention.

FIG. 10 is a longitudinal sectional view showing a side lock chuckingstructure according to a modification of the present invention.

FIG. 11 is a longitudinal sectional view showing a side lock chuckingstructure according to another modification of the present invention.

FIG. 12 is a perspective view showing a shank portion of an end millaccording to a modification of the present invention.

FIG. 13 is an overall view showing a tool holder according to stillanother embodiment of the present invention.

FIG. 14 is an overall view showing a tool holder according to a furtherembodiment of the present invention.

FIG. 15 is an overall view showing a tool holder according to a stillfurther embodiment of the present invention.

FIG. 16 is an overall view showing a tool holder according to a yetfurther embodiment of the present invention.

FIG. 17 is an overall view showing the state where the tool holder ofFIG. 16 is not holding a shank portion.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described in detail belowwith reference to the accompanying drawings. FIG. 1 is a side viewshowing an end mill according to an embodiment of the present invention.FIG. 2 is an overall view showing a tool holder according to anembodiment of the present invention. FIG. 3 is a transverse sectionalview showing the tool holder and the end mill of the embodiment takenalong line III-III in FIG. 2, as viewed from the direction shown by anarrow. FIG. 4 is a front view showing an axial tip end of the toolholder of the embodiment. FIG. 5 is a front view showing the axial tipend of the tool holder of the embodiment having a lid member removedtherefrom. FIG. 6 is an overall view showing a groove formed in an innerperipheral surface of a tool attaching/detaching portion of the toolholder of the embodiment. FIG. 7 is an overall view showing the toolholder of the embodiment before chucking, which is not holding a shankportion of the end mill. In FIGS. 2, 6, and 7, the upper half of thetool holder is shown by a longitudinal sectional view, and the lowerhalf of the tool holder is shown by a side view. The cross section inFIG. 2 and the cross section in FIG. 6 are taken along chain lines II-IIand VI-VI in FIG. 4, respectively.

An end mill 60 is made of steel, and has a cutting portion 60 b in anaxial tip end region (as used herein, the term “axial” refers to thedirection of an axis O″), and has a shank portion 61 in an axial rearend region. The cutting portion 60 b is made of a super steel alloy. Theshank portion 61 is basically a cylindrical portion having a circularcross section with a constant radius, but has two flat surfaces(hereinafter referred to as the “first flat surface 62” and the “secondflat surface 63”) formed in its outer periphery by a cutting process.

As shown in FIG. 1, the first flat surface 62 and the second flatsurface 63 are provided in the axial rear end of the shank portion 61.As shown in FIG. 2, the first flat surface 62 is not parallel to theaxis O of the shank portion 61, but is slightly tilted so as to facetoward the tip end of the end mill 60. The tilt angle of the first flatsurface 62 is 5 degrees with respect to the axis O. Alternatively, thefirst flat surface 62 is a surface tilted at an angle in the range of 1to 10 degrees. The second flat surface 63 is formed in a manner similarto that of the first flat surface 62.

As shown in FIG. 3, the first flat surface 62 is provided at a positionof 90 degrees about the axis O of the shank portion 61 with respect tothe second flat surface 63. Alternatively, the first flat surface 62 isprovided at a position of 80 to 100 degrees about the axis O of theshank portion 61 with respect to the second flat surface 63. “90degrees” shown in FIG. 3 is an angle from the center in thecircumferential direction of the first flat surface 62 to the center inthe circumferential direction of the second flat surface 63.

A tool holder 10 includes as main components a holder body 11, first andsecond side lock bolts 23 a, 23 b, and a fastening member 32.

The holder body 11 is made of a metal, and extends along the axis Oshown by chain line. The holder body 11 has in an axial tip end region atool attaching/detaching portion 12 that chucks the end mill 60, and hasin an axial rear end region a mount portion 13 that is mounted on a mainshaft of a machine tool. A flange portion 14 having a large diameter isformed in a central portion in the direction of the axis O of the holderbody 11 so as to protrude radially outward beyond the toolattaching/detaching portion 12 and the mount portion 13. A V-shapedgroove 142 extending in the circumferential direction is formed in anouter peripheral edge of the flange portion 14. A drive key groove 143extending in the axial direction is also formed in the outer peripheraledge of the flange portion 14.

The mount portion 13 is shaped so as to fit on the main shaft of themachine tool, not shown. The outer peripheral surface of the mountportion 13 of the present embodiment is tapered so that the radius ofthe outer peripheral surface of the mount portion 13 decreases towardthe rear end in the axial direction of the mount portion 13. The mountportion 13 has a central hole 132 extending along the axis O as thecenter of the holder body 11. The central hole 132 extends from theaxial rear end of the holder body 11 toward the axial tip end thereof,and has several different inner diameters at intermediate positions inthe axial direction. The innermost part of the central hole 132, whichis located closest to the axial tip end of the holder body 11, is asmall central hole 133 having a small diameter. A main shaft-sidemember, not shown, fits in the axial rear end of the central hole 132.The mount portion 13 is pulled rearward by the main shaft-side member,whereby the mount portion 13 is firmly mounted on a center throughcoolant main shaft of the machine tool. Then, cutting fluid or cleaningfluid flows into the central hole 132 from the center through coolantmain shaft. Thus, the central hole 132 serves as a fluid passage.

The tool attaching/detaching portion 12 has a cylindrical shape havingan opening in its axial tip end, and has an outer peripheral surface andan inner peripheral surface 12 h. The inner peripheral surface 12 hdefines and forms a tool holding hole 122 extending along the axis Ofrom the axial tip end of the tool attaching/detaching portion 12 towardthe axial rear end thereof. The tool holding hole 122 has a constantinner diameter, and has a bottom 123. The tool holding hole 122 connectsto the small central hole 133 formed in the bottom 123. This allows thecutting fluid to flow from the central hole 123 onto the bottom 123 ofthe tool holding hole 122.

As shown in FIG. 2, a circumferential groove 124 is formed in the innerperipheral surface 12 h of the tool attaching/detaching portion 12. Asshown in FIG. 6, grooves 126 are formed in the inner peripheral surface12 h of the tool attaching/detaching portion 12. The grooves 126 extendfrom an axial tip end face 125 of the tool attaching/detaching portion12 toward the axial rear end thereof, and connect to the peripheralgroove 124. The cutting fluid, which has flown from the small centralhole 133 onto the bottom of the tool holding hole 122, flows along thegrooves 126 through the circumferential groove 124, and flows toward theaxial tip end face 125. As a modification, the circumferential groove124 may not be formed in the inner peripheral surface 12 h.

To be exact, the grooves 126 do not extend parallel to the axis O, butare tilted in the circumferential direction as shown by solid line inFIG. 2 and broken line FIG. 5. For convenience, the entire length of onegroove 126 is shown in FIG. 6, and the other grooves 126 are not shownin FIG. 6.

The axial tip end face 125 is covered by a lid member 41. As shown inFIG. 4, the lid member 41 is a ring-shaped plate material, and has endfaces on both sides in the direction of the axis O of the tool holder10. The outer peripheral edge of the lid member 41 protrudes radiallyoutward beyond the axial tip end face 125. A plurality of through holes414 are formed in the lid member 41 at predetermined intervals in thecircumferential direction. Bolts 44 are inserted through the throughholes 414 from the side of the axial tip end, and the tip ends of thebolts 44 are screwed in bolt holes 127 (FIGS. 2 and 5) formed in theaxial tip end face 125, whereby the lid member 41 is attached and fixedto the axial tip end of the tool attaching/detaching portion 12.

As shown in FIG. 4, injection ports 415 in the shape of a triangulargroove are formed in the inner peripheral edge of the lid member 41 soas to extend from the tip end face of the lid member 41 to the rear endface thereof. When the lid member 41 is fixed to the axial tip end ofthe tool attaching/detaching portion 12, the injection ports 415 arealigned with the axial tip ends of the grooves 126, as shown in FIG. 6.When the shank portion 61 of the end mill 60 is inserted in the toolholding hole 122 so that the shank portion 61 having a circular crosssection is chucked by the tool attaching/detaching portion 12, thegrooves 126 and the injection ports 415 form continuous fluid passages.The cutting fluid flowing along the grooves 126 is injected from theinjection ports 415 toward the tip end of the end mill 60, and reaches aworkpiece (an object to be cut), not shown. Thus, the grooves 126functions as cutting fluid passages. The grooves 126 also facilitateelastic deformation of the tool attaching/detaching portion 12 in thedirection in which the diameter of the tool attaching/detaching portion12 is reduced. The number of grooves 126 is preferably larger than one,and may be larger than that of grooves 126 in the embodiment shown inFIG. 5.

The tool holder 10 has a side lock chucking structure 21 and a roll lockchucking structure 31 in the tool attaching/detaching portion 12 as astructure that chucks the shank portion 61 of the end mill 60. The rolllock chucking structure 31 corresponds to a centering holding unit thatcenters and holds the shank portion 61 of the end mill 60. The side lockchucking structure 21 has a function to provide final fastening, namelya function to chuck the shank portion 61 of the end mill 60 which hasbeen centered and held.

The side lock chucking structure 21 will first be described. An outerperipheral surface 12 a of a tip end portion of the toolattaching/detaching portion 12 has a small diameter, and an outerperipheral surface 12 b of a rear end portion of the toolattaching/detaching portion 12 has a large diameter. An annular steppedsurface 12 c is formed between the tip end outer peripheral surface 12 aand the rear end outer peripheral surface 12 b. Two through holes 22 a,22 b are formed in the rear part of the tool attaching/detaching portion12. The first through hole 22 a extends from the rear end outerperipheral surface 12 b of the tool attaching/detaching portion 12 tothe inner peripheral surface 12 h of the tool attaching/detachingportion 12, and connects to the tool holding hole 122. The first throughhole 22 a extends substantially in the radial direction of the toolattaching/detaching portion 12, but as shown in FIG. 2, is slightlytilted so that the outer-diameter side of the first through hole 22 a islocated closer to the axial tip end of the tool attaching/detachingportion 12 than the inner-diameter side of the first through hole 22 a.The tilt angle of the first through hole 22 a is 5 degrees with respectto the direction at right angles to the axis O of the holder member 11.Alternatively, the tilt angle of the first through hole 22 a is in therange of 1 to 10 degrees so as to correspond to the tilt angle of thefirst flat surface 62.

The second through hole 22 b is provided in a manner similar to that ofthe first through hole 22 a. The second through hole 22 b extendssubstantially in the radial direction of the tool attaching/detachingportion 12, but is slightly tilted so that the outer-diameter side ofthe second through hole 22 b is located closer to the axial tip end ofthe tool attaching/detaching portion 12 than the inner-diameter side ofthe second through hole 22 b. The tilt angle of the second through hole22 b is 5 degrees with respect to the direction at right angles to theaxis O of the holder member 11. Alternatively, the tilt angle of thesecond through hole 22 b is in the range of 1 to 10 degrees so as tocorrespond to the tilt angle of the second flat surface 63. The throughholes 22 a, 22 b are placed at the same axial position, and thecircumferential groove 124 is formed at the axial position of thethrough holes 22 a, 22 b.

The through hole 22 a is provided at a position of 90 degrees about theaxis O of the holder body 11 with respect to the through hole 22 b.Alternatively, the angle from the through hole 22 a to the through hole22 b is in the range of 80 to 100 degrees so as to correspond to theangle from the first flat surface 62 to the first flat surface 63.

The first through hole 22 a has an internally threaded portion 22 s nearthe tool holding hole 122. An outer-diameter portion 22 m of the firstthrough hole 22 a, which is located far from the tool holding hole 122,has a larger inner diameter than the internally threaded portion 22 s.The first side lock bolt 23 a is screwed into the first through hole 22a from the outer-diameter side. The second through hole 22 b isconfigured in a manner similar to that of the first through hole 22 a,and the second side lock bolt 23 b is screwed into the second throughhole 22 b from the outer-diameter side.

The first side lock bolt 23 a has a head portion 23 m in itslongitudinal rear end, and has an externally threaded portion 23 s inits longitudinal central region. The longitudinal tip end of the sidelock bolt 23 a has a smaller diameter than the externally threadedportion 23 s, and the side lock bolt 23 a has a tip end face 23 t thatis a flat surface perpendicular to the longitudinal direction of theside lock bolt 23 a. The head portion 23 m is accommodated in theouter-diameter portion 22 m, and the externally threaded portion 23 s isscrewed in the internally threaded portion 22 s. The tip end of the sidelock bolt 23 a protrudes from the through hole 22 a into the toolholding hole 122.

An annular groove is formed in the outer periphery of the head portion23 m of the side lock bolt 23 a, and an O-ring 24 as an annular sealingmember engages with the annular groove. The O-ring 24 contacts theouter-diameter portion 22 m of the through hole 22 a along the entirecircumference. Thus, the O-ring 24 seals the annular gap between thethrough hole 22 a and the side lock bolt 23 a.

The second side lock bolt 23 b is configured in a manner similar to thatof the first side lock bolt 23 a.

A recess 25 a is provided in the rear end outer peripheral surface 12 bof the tool attaching/detaching portion 12 at a differentcircumferential position from the through hole 22 a. The recess 25 aserves to prevent the center of gravity of the holder body 11 from beingshifted from the axis O due to the formation of the through hole 22 a.As shown in FIG. 3 as a simple embodiment, the recess 25 a is formed ata position of 180° in the circumferential direction with respect to thethrough hole 22 a. Thus, the center of gravity of the holder body 11 isaligned with the axis O, and the mass about the axis O can be balanced.Similarly, a recess 25 b is provided in the rear end outer peripheralsurface 12 b of the tool attaching/detaching portion 12 at a differentcircumferential position from the through hole 22 b. As anotherembodiment, a recess or a mass adjusting portion made of a mass body isformed at a position of an angle other than 180° in the circumferentialdirection with respect to the through hole 22 a, 22 b.

The recesses 25 a, 25 b may be provided to balance the mass of theholder body 11 and the side lock bolts 23 a, 23 b about the axis in thestate where the shank portion 61 of the end mill 60 inserted in the toolholding hole 122 is fixed by the side lock bolts 23 a, 23 b. Thus, thecenter of gravity of an assembly of the side lock bolts 23 a, 23 brotated in the fastening direction until the shank portion 61 of the endmill 60 is fixed and the holder body 11 having the through holes 22 a,22 b can be approximately aligned with the axis O or can be aligned withthe axis O. This can prevent displacement of the axis of the cuttingportion 60 b provided at the tip end of the end mill 60, and theworkpiece can be processed with high accuracy.

The roll lock chucking structure 31 will be described below. The tip endouter peripheral surface 12 a of the tool attaching/detaching portion 12has a circular cross section about the axis O, is tapered so that thediameter of the tip end outer peripheral surface 12 a decreases towardthe axial tip end (e.g., 1/32 taper), and is surrounded by the fasteningmember 32.

The fastening member 32 reduces the diameter of the toolattaching/detaching portion 12 and tightly holds the shank portion 61 ofthe end mill 60 so that the entire outer periphery of the shank portion61 of the end mill 60 closely contacts the inner peripheral surface 12 halong its entire circumference. An inner peripheral surface 32 a of thefastening member 32 is tapered at the same angle as the tip end outerperipheral surface 12 a (e.g., 1/32 taper), and faces the tip end outerperipheral surface 12 a. A retaining ring 36 is attached to the innerperipheral surface of a rear end portion of the fastening member 32. Ifthe fastening member 32 moves toward the axial tip end, the innerperipheral edge of the retaining ring 36 abuts on an engagement portionformed in the tip end outer peripheral surface 12 a, thereby restrictingfurther movement of the fastening member 32 toward the axial tip end.This prevents the fastening member 32 from coming off from the toolattaching/detaching portion 12.

A plurality of needle rollers 34 and a retainer 35 that aligns theneedle rollers 34 are placed in an annular space 33 formed between theinner peripheral surface 32 a of the fastening member 32 and the tip endouter peripheral surface 12 a of the tool attaching/detaching portion12. The retainer 35 is formed in the form of a cylinder body tapered atthe same angle as the tip end outer peripheral surface 12 a, and isloosely fitted on the tip end outer peripheral surface 12 a.

The thickness dimension of the retainer 35 is smaller than the intervalbetween the inner peripheral surface 32 a and the tip end outerperipheral surface 12 a, i.e., the diameter of the needle rollers 34. Aplurality of pockets, each holding one or more of the needle rollers 34,are formed in the retainer 35 at predetermined intervals in thecircumferential direction and at predetermined intervals in the axialdirection. The pockets are rectangular holes that extend through theretainer 35 in the radial direction. Rolling surfaces of the needlerollers 34 protrude from the pockets radially inward of the retainer 35,and contact the tip end outer peripheral surface 12 a. The rollingsurfaces of the needle rollers 34 also protrude from the pocketsradially outward of the retainer 35, and contact the inner peripheralsurface 32 a.

The pockets of the retainer 35 are tilted at a predetermined angle inthe circumferential direction with respect to the central axis. Thus,the needle rollers 34 held by the pockets are tilted at thepredetermined angle in the circumferential direction with respect to theaxis O, and roll on the tip end outer peripheral surface 12 a so as tomake a helical track.

The fastening member 32 is made of a metal, and the axial tip edge ofthe fastening member 32 protrudes beyond the axial tip end face 125 ofthe tool attaching/detaching portion 12 toward the axial tip end. Theaxial tip edge of the fastening member 32 faces the outer peripheraledge of the lid member 41. The outer-diameter dimension of the lidmember 41 is larger than that of the axial tip end face 125, and the lidmember 41 covers an opening at the axial tip end of the annular space 33between the fastening member 32 and the tool attaching/detaching portion12. Thus, the outer peripheral edge of the lid member 41 restrictsmovement of the retainer 35 toward the axial tip end, and the retainer35 does not come off from the tool attaching/detaching portion 12.

An O-ring 42 as an annular outer-peripheral sealing member is attachedto the outer peripheral edge of the lid member 41. The O-ring 42 sealsbetween the lid member 41 and the fastening member 32. This preventsforeign matter from entering the annular space 33.

The axial rear edge of the fastening member 32 is formed in an annularflat surface 32 c perpendicular to the axis O, and faces the annularstepped surface 12 c of the holder body 11. The fastening member 32 ismovable in the axial direction in a region located on the tip end sideof the annular stepped surface 12 c. The annular stepped surface 12 crestricts rearward movement in the axial direction of the fasteningmember 32 so as not to allow the fastening member 32 to move toward therear end beyond the annular stepped surface 12 c. An annular groove isformed in the annular flat surface 32 c, and an O-ring 37 as an annularsealing member is attached to the annular groove.

An annular groove 12 d about the axis O is formed on an inner-diameterportion of the annular stepped surface 12 c. A side surface on theinner-diameter side of the annular groove 12 d has the same diameter asthe tip end outer peripheral surface 12 a, and is continuous with thetip end outer peripheral surface 12 a, thereby increasing the axialdimension of the tip end outer peripheral surface 12 a. Thus, aneffective holding length L1 of the roll lock chucking structure 31 canbe increased without increasing the length of the holder body 11.

In the operation of chucking the end mill 60, the shank portion 61 ofthe end mill 60 is first inserted into the tool holding hole 122, theshank portion 61 is then held with high accuracy by the roll lockchucking structure 31, and thereafter rotation of the shank portion 61is prevented by the side lock chucking structure 21. According to thepresent embodiment, in a former part of the operation, the fasteningmember 32 is rotated to reduce the diameter of the tool holding hole122, and the shank portion 61 of the end mill 60 is held by thefastening member 32, whereby the axis of the end mill 60 is aligned withthe axis of the holder body 11, and the shank portion 61 of the end mill60 can be held with high accuracy by the tool attaching/detachingportion 12. In a later part of the operation, the two side lock bolts 23a, 23 b are fastened, whereby the shank portion 61 of the end mill 60,which has been held with high accuracy so as to be aligned with the axisO, can be prevented from rotating without being displaced from the axisO. If the former and later parts of the operation are performed inreverse order, the shank portion of the end mill cannot be held withhigh accuracy.

The chucking operation will be described in detail below. As shown inFIG. 10, the side lock bolts 23 a, 23 b are rotated in advance in theloosening direction so that the tip ends of the side lock bolts 23 a, 23b are withdrawn from the tool holding hole 122. The fastening member 32is rotated in the loosening direction to restore the toolattaching/detaching portion 12 radially outward, thereby increasing theinner-diameter dimension of the tool holding hole 122. Next, the shankportion 61 of the end mill 60 is inserted into the tool holding hole 122from the side of the axial tip end. Since a part of the outer peripheryof the shank portion 61 has been cut to form the first and second flatsurfaces 62, 63 having a phase difference of about 90 degrees from eachother. Thus, the end mill 60 is pivoted so that the first flat surface62 faces the through hole 22 a. At this time, the second flat surface 63also faces the through hole 22 b.

Then, the fastening member 32 is rotated in the fastening direction, andthe needle rollers 34, which are in contact with the inner peripheralsurface 32 a of the fastening member 32, revolve in a helical pattern onthe tip end outer peripheral surface 12 a while rotating. Thus, thefastening member 32 together with the retainer 35 gradually moves towardthe axial rear end. Accordingly, due to the wedging action of thetapered inner peripheral surface 32 a and the tapered outer peripheralsurface 12 a, the outer peripheral surface 12 a is strongly pressedradially inward along its entire circumference and is reduced indiameter. As a result, the tool holding hole 122 formed in the center ofthe tool attaching/detaching portion 12 is also reduced in diameter, anda cylindrical portion as the front part of the shank portion 61 insertedin the tool holding hole 122 is fastened uniformly along its entirecircumference by the inner peripheral surface 12 h in the effectiveholding length L1 of the tip end outer peripheral surface 12 a.Accordingly, the tool attaching/detaching portion 12 holds the outerperipheral surface of the shank portion 61 uniformly in thecircumferential direction. Thus, the shank portion 61 is tightly andfirmly held by an axial region of the tool attaching/detaching portion12, and the axis of the holder body 11 is aligned with the axis of theend mill 60, whereby the end mill 60 is held with high accuracy alongthe axis O.

When the fastening member 32 is rotated in the fastening direction tohold the shank portion 61, the annular flat surface 32 c at the axialrear end of the fastening member 32 abuts on the annular stepped surface12 c of the holder body 11, and the O-ring 37 is interposed between theaxial rear edge of the fastening member 32 and the annular steppedsurface 12 c of the holder body 11. Thus, the opening in the axial rearend of the annular space 33 between the fastening member 32 and the toolattaching/detaching portion 12 can be sealed, whereby foreign matter isprevented from entering the annular space 33.

Thereafter, both of the side lock bolts 23 a, 23 b are rotated in thefastening direction so that the tip end face 23 t of the side lock bolt23 a screwed into the through hole 22 a abuts on the first flat surface62 and that the tip end face 23 t of the side lock bolt 23 b screwedinto the through hole 22 b abuts on the second flat surface 63. The flattip end face 23 t of the side lock bolt 23 a presses with a strong forcethe first flat surface 62 in the rear part of the shank portion 61, andthe flat tip end face 23 t of the side lock bolt 23 b presses with astrong force the second flat surface 63 in the rear part of the shankportion 61, thereby fixing the shank portion 61 in the tool holding hole122. Since the circumferential groove 124 is formed at the same axialposition as the through holes 22 a, 22 b, the cutting fluid flowing fromthe central hole 132 toward the axial tip end flows into thecircumferential groove 124 on the side of the axial rear end withrespect to the cylindrical portion in the front part of the shankportion 61. Thus, the cutting fluid smoothly flows into the grooves 126.

As described above, the shank portion 61 is first held by using the rolllock chucking structure 31, and then rotation of the shank portion 61 isprevented by using the side lock chucking structure 21, whereby theshank portion 61 is chucked by the tool attaching/detaching portion 12as shown in FIGS. 2 and 3. The operation described above is performed inreverse order in order to remove the end mill 60.

Another embodiment of the present invention will be described below.FIG. 8 is a side view showing an end mill according to anotherembodiment of the present invention. FIG. 9 is a longitudinal sectionalview showing a tool holder that chucks the end mill of FIG. 8. In thisembodiment, the same configurations as those of the above embodiment aredenoted with the same reference characters, and description thereof isomitted. Configurations different from the above embodiment will bedescribed below.

An end mill 65 according to this embodiment has the same basicconfiguration as the end mill 60, and further includes a fluid passage66 extending from the shank portion 61 toward the tip end of the endmill 65.

A tool holder 20 of this embodiment has the two side lock bolts 23 a, 23b described above, and further has an O-ring 43 as an annular innerperipheral sealing member that seals between the inner peripheral edgeof the lid member 41 and the outer peripheral surface of the shankportion 61 of the end mill 65 inserted in the tool holding hole 122. Thefluid passage 66 extending from the rear end of the end mill 65 towardthe tip end thereof is formed in the shank portion 61 that is chucked bythe tool holder 20, and cutting fluid is supplied from the small centralhole 133 to the rear end of the fluid passage 66 via the tool holdinghole 122. The cutting fluid flows through the fluid passage 66, isinjected from the tip end (not shown) of the end mill 65, and reaches aworkpiece. According to the embodiment of FIG. 9, the tool holder 20includes the annular O-ring 43 that seals between the inner peripheraledge of the lid member 41 and the outer peripheral surface of the shankportion 61. Thus, the cutting fluid flowing from the small central hole133 into the tool holding hole 122 can be prevented from leaking fromthe tip end of the tool attaching/detaching portion 12. In particular,the O-ring 43 is effective in the case where the grooves 126 describedabove are formed in the inner peripheral surface 12 h of the tool holder20.

The tool holder 20 according to this embodiment further includes astopper member 51 provided on the bottom side of the tool holding hole122. The stopper member 51 defines the axial position of the shankportion 61 of the end mill 65 inserted in the tool holding hole 122.

The stopper member 51 includes a fixing member 52 that is fixed to theinner peripheral surface 12 h of the tool attaching/detaching portion12, and an adjuster member 53 that is supported by the fixing member 52so as to be displaceable in the axial direction and that abuts on theshank portion 61 of the end mill 65. An externally threaded portion 522is formed in the outer peripheral surface of the fixing member 52, andis screwed in an internally threaded portion 12 s formed in the innerperipheral surface 12 h of the tool attaching/detaching portion 12 nearthe bottom of the tool holding hole 122. Thus, the fixing member 52 isattached and fixed to the tool holding hole 122. An annular groove isformed in the outer peripheral surface of the fixing member 52 at aposition closer to the tip end than the externally threaded portion 522.An O-ring 55 as an annular sealing member is attached to the annulargroove. The O-ring 55 is a first sealing member that seals between thetool holding hole 122 and the fixing member 52.

A central hole 523 is also formed so as to extend through the fixingmember 52 in the axial direction, and the adjuster member 53 is attachedand fixed to the central hole 523. The rear end side of the central hole523 has a smaller diameter than the tip end side thereof, and aninternal threaded portion 524 is formed in the rear end side of thecentral hole 523.

The adjuster member 53 is formed by a tip end 531 having a largediameter, a central portion 534 having a smaller diameter than the tipend 531, and a rear end 535 having a smaller diameter than the centralportion 534, and is shaped so that three cylinders are coupled togetherin series. A communication passage 532 is formed in the center of theadjuster member 53 so as to extend through the adjuster member 53 in theaxial direction. The opening at the rear end of the communicationpassage 532 connects to the small central hole 133. The opening at thetip end of the communication passage 532 connects to the opening at therear end of the fluid passage 66 of the shank portion 61.

The adjuster member 53 has the tip end 531 having a large diameter, andthe tip end 531 has a tip end face 533 having a large diameter. The tipend face 533 abuts on the rear end of the shank portion 61 of the endmill 65 inserted in the tool holding hole 122, so that the tip end face533 surface contacts the rear end of the shank portion 61 of the endmill 65. The tip end face 533 thus defines the axial position of theshank portion 61. A ring groove is formed about the axis O in the tipend face 533, and an annular O-ring 57 is attached to the ring groove.The O-ring 57 is a third sealing member that contacts the rear end faceof the shank portion 61 with no gap therebetween and seals between thetip end face 533 and the shank portion 61. Thus, the opening at the tipend of the communication passage 532, which is provided in the center ofthe tip end face 533, connects in a hermetically sealed manner to theopening at the rear end of the liquid passage 66, which is provided inthe center of the rear end face of the shank portion 61.

An externally threaded portion is formed in the outer peripheral surfaceof the rear end 535 of the adjuster member 53, and is screwed in aninternally threaded portion 524 of the fixing member 52. By suchscrewing, the axial position of the adjuster member 53 is adjusted asshown by broken line in FIG. 9 by rotating the adjuster member 53.

The central portion 534 of the adjuster member 53 is received by the tipend of the central hole 523 of the fixing member 52. An annular grooveis formed in the outer peripheral surface of the central portion 534 ofthe adjuster member 53, and an O-ring 56 as an annular sealing member isattached to the annular groove. The O-ring 56 is a second sealing memberthat seals between the inner peripheral surface of the fixing member 52and the outer peripheral surface of the adjuster member 53.

According to the embodiment shown in FIG. 9, the central hole 132 andthe small central hole 133 as a fluid passage through which the cuttingfluid flows extend from the mount portion 13 of the holder body 11 tothe bottom 123 of the tool holding hole 122. The adjuster member 53 isattached and fixed to the central hole 523 that extends through thefixing member 52 in the axial direction. The adjuster member 53 has thecommunication passage 532 that allows the bottom 123 of the tool holdinghole 122 to communicate with the opening of the tool holding hole 122,and the annular O-ring 57 that seals between the tip end face 533 as theaxial tip end face of the adjuster member 53 and the rear end face ofthe shank portion 61 of the end mill 65. This allows the small centralhole 133 of the holder body 11 to reliably communicate with the fluidpassage 66 of the end mill 65 through the communication passage 532.

The fixing member 52 has the annular O-ring 55 that seals between thefixing member 52 and the tool holding hole 122. The adjuster member 53has the annular O-ring 56 that seals between the peripheral wall surfaceof the central hole 523 and the adjuster member 53. Thus, the cuttingfluid can be prevented from flowing out toward the through holes 22 a,22 b.

A modification of the side lock chucking structure will be describedbelow with reference to the longitudinal sectional view of FIG. 10. Inthe modification, an annular groove is formed in the outer-diameterportion 22 m of the through hole 22 a, and a snap ring 26 is attachedand fixed to the annular groove. The snap ring 26 is a C-shapedretaining member that is located radially outward of the side lock bolt23 a, and that prevents the side lock bolt 23 a from coming off outward(radially outward) from the through hole 22 a. Thus, even if the sidelock bolt 23 a loosens during high-speed rotation of the tool holder 10,the side lock bolt 23 a can be prevented from coming off from thethrough hole 22 a. The snap ring 26 is also provided in the through hole22 b in a manner similar to that in the through hole 22 a.

FIG. 10 shows the state where the side lock bolt 23 a is rotated in theloosening direction so that the head portion 23 m of the side lock bolt23 a abuts on the snap ring 26. Thus, if the side lock bolt 23 a ismoved radially outward, the tip end face 23 t of the side lock bolt 23 awithdraws out of the tool holding hole 122. According to thismodification, the shank portion 61 having a cylindrical shape and havingno abutting flat surface formed therein as a cut-out surface can beinserted into the tool holding hole 122. Note that the shank portion 61can be held by the roll lock chucking structure 31.

Another modification of the side lock chucking structure will bedescribed with reference to the longitudinal sectional view of FIG. 11.In the modification shown in FIG. 11, the side lock bolt 23 a includes abolt body 231 and a pressing member 232. The bolt body 231 has in itslongitudinal rear end a head portion 23 m having a large diameter, andhas in its longitudinal central region an internally threaded portion 34s having a small diameter. A spherical recess is formed in thelongitudinal tip end of the bolt body 231, and the pressing member 232having a ball shape fits in the recess 23. A flat pressing surface 23 tis formed at the tip end of the pressing member 232. Since the pressingmember 232 is thus supported by the spherical surface of the bolt body231, the pressing surface 23 t can be rotated about the central axis ofthe bolt body 231, and can be tilted with respect to the central axis ofthe bolt body 231. Accordingly, orientation of the pressing member 232with respect to the bolt body 231 can be changed as desired. In additionto the modification of FIG. 12, attachment of the pressing member 232 tothe bolt body 231 may be implemented by any method such as a universaljoint as long as the orientation of the pressing member 232 can bechanged as desired.

When the bolt body 231 is screwed into the internally threaded portion22 s of the through hole 22 a and is rotated in the fastening direction,the side lock bolt 23 a advances into the tool holding hole 122, and thepressing surface 23 t of the side lock bolt 23 a abuts on the first flatsurface 62. If the bolt body 231 is further rotated in the fasteningdirection, the pressing surface 23 t changes its orientation accordingto the first flat surface 62, and surface contacts the first flatsurface 62.

As described above, according to the modification of FIG. 11, even ifthe first flat surface 62 of the shank portion 61 is not exactlyperpendicular to the direction in which the side lock bolt 23 aadvances, the pressing surface 23 t of the pressing member 232 changesits orientation according to the first flat surface 62 of the shankportion 61, and surface contacts the first flat surface 62. Thus, theside lock bolt 23 a firmly presses the first flat surface 62 of theshank portion 61, whereby the shank portion 61 can be more reliablychucked. The second side lock bolt 23 b can be configured in a mannersimilar to that of the first side lock bolt 23 a.

A shank portion of an end mill according to a modification of thepresent invention will be described with reference to the perspectiveview of FIG. 12. In the modification shown in FIG. 12, the first flatsurface 62 and the second flat surface 63 have been surface-treated soas to have a higher friction coefficient. Specifically, the first flatsurface 62 and the second flat surface 63 have a fine concavo-convexprofile by shot peening.

Shot peening is a cold processing method in which many particles aredirected onto a surface to be processed, thereby forming many concavesand convexes on the surface to be processed. Since the first flatsurface 62 and the second flat surface 63 which have been subjected tothe shot peening have a residual compressive stress, fatigue life isincreased.

As described above, according to the modification of FIG. 12, at leastone of the first flat surface 62 and the second flat surface 63 has beensurface-treated so as to have a higher friction coefficient.Accordingly, when the first flat surface 23 a abuts on the side lockbolt 23 a, the tip end face (the pressing surface) 23 t of the side lockbolt 23 a is less likely to slide on the first flat surface 62, wherebythe side lock bolt 23 a can reliably press the first flat surface 62.This makes it more difficult for the shank portion 61 to come off fromthe tool holder 10, 20.

Instead of surface-treating the first flat surface 62 and the secondflat surface 63 in the manner described above, the tip end face (thepressing surface) 23 t of the side lock bolt 23 a may be surface-treatedso as to have a higher friction coefficient. According to such amodification as well, the tip end face (the pressing surface) 23 t ofthe side lock bolt 23 a is less likely to slide on the first flatsurface 62, whereby the side lock bolt 23 a can reliably press the firstflat surface 62. This makes it more difficult for the shank portion 61to come off from the tool holder 10, 20. Moreover, in this modification,the processing is simpler as compared to the case where the first flatsurface 62 and the second flat surface 63 are surface-treated in themanner described above. The tip end face (the pressing surface) of theside lock bolt 23 b may also be surface-treated so as to have a higherfriction coefficient.

Still another embodiment of the present invention will be describedbelow. FIG. 13 is an overall view showing a tool holder according tostill another embodiment of the present invention. In FIG. 13, the upperhalf of the tool holder is shown by a longitudinal sectional view. Inthis embodiment, the same configurations as those of the aboveembodiments are denoted with the same reference characters, anddescription thereof is omitted. Configurations different from the aboveembodiments will be described below.

A tool holder 30 has a side lock chucking structure 21 and a tapercollet chucking structure 71 in the tool attaching/detaching portion 12as a structure that chucks the shank portion 61 of the end mill 60. Thetaper collet chucking structure 71 corresponds to a centering holdingunit that centers and holds the shank portion 61 of the end mill 60. Theside lock chucking structure 21 has a function to provide finalfastening, namely a function to chuck the shank portion 61 of the endmill 60 which has been centered and held.

The taper collet chucking structure 71 has a tapered hole 72, a tapercollet 73, a lock nut 78, and a plane bearing 70. The tapered hole 72 isformed in the tool attaching/detaching portion 12, and extends rearwardfrom the tip end of the holder body 11 along the axis O. The innerdiameter of the tapered hole 72 increases from the rear end of thetapered hole 72 toward the tip end thereof.

The taper collet 73 having a cylindrical shape fits in the tapered hole72. The inner periphery of the taper collet 73 is a tool insertion hole73 h. The tool insertion hole 73 h extends through the taper collet 73from the rear end of the taper collet 73 to the tip end thereof in theaxial direction. The shank portion 61 of the end mill 60 is insertedinto the tool insertion hole 73 h from the tip end side of the toolinsertion hole 73 h. A rear end portion of the outer periphery of thetaper collet 73 is a tapered surface 73 t whose diameter is reducedtoward the rear end. The tapered surface 73 t fits in the tapered hole72.

A ring groove 74 is formed in the outer periphery of the taper collet73, which adjoins the tip end of the tapered surface 73 t, so as toextend along the entire circumference of the taper collet 73. An outerperiphery 75 of the tip end of the taper collet 73 which adjoins the tipend of the ring groove 74 has a larger diameter than the ring groove 74.The side surface on the rear end side of the ring groove 74, i.e., theboundary between the ring groove 74 and the tapered surface 73 t, formsan annular flat surface 73 k perpendicular to the axis O.

The taper collet 73 has slit-shaped slots 76 extending parallel to theaxis O. At least one of the slots 76 extends from the tip end of thetaper collet 73 to an intermediate position thereof, and the remainderof the slots 76 extends from the rear end of the taper collet 73 to anintermediate position thereof. All the slots 76 are arranged at regularintervals in the circumferential direction. The diameter of the tapercollet 73 can be changed by compressing the slots 76.

An internally threaded portion 78 m is formed in the inner periphery ofthe lock nut 78 having a cylindrical shape, and an externally threadedportion 12 m is formed in the outer periphery of the toolattaching/detaching portion 12. The internally threaded portion 78 m isscrewed on the externally threaded portion 77. The lock nut 78 is amember that is screwed on the holder body 11 to press the taper collet73 toward the axial rear end. The taper collet 73 is pressed in thetapered hole 72, and the diameter of the tool insertion hole 73 h isreduced.

The lock nut 78 has a cylindrical portion 79 and an inward flangeportion 80. The cylindrical portion 79 has the internally threadedportion 78 m formed in its inner periphery so as to be screwed on anexternally threaded portion 12 m formed in the outer periphery of thetip end of the holder body 11. The inward flange portion 80 is formed inthe tip end of the cylindrical portion 79 so as to protrude radiallyinward. A flat surface 80 k on the rear end side of the inward flangeportion 80 is an annular flat surface extending at right angles to theaxis O. The inner peripheral edge of the inward flange portion 80engages with the ring groove 84 of the taper collet 73. The planebearing 70 is inserted between the flat surface 80 k on the rear endside of the inward flange portion 80 and the flat surface 73 k of thetaper collet 73.

The plane bearing 70 is a type of plain bearing that transmits a forcein the direction of the axis O while reducing friction in the directionat right angles to the axis O, and is a plate material in the shape of aring board having an outer diameter corresponding to the diameter of theinner periphery of the lock nut 78. The inner peripheral edge of theplane bearing 70 engages with the ring groove 74. The end face on therear end side of the plane bearing 70 contacts the flat surface 73 k ofthe taper collet 73, and the end face on the tip end side of the planebearing 70 contacts the flat surface 80 k on the rear end side of theflange portion 80. The plane bearing 70, which receives the pressingforce in the direction of the axis O between the inward flange portion80 and the taper collet 73, reduces the frictional resistance of bothcontact surfaces (the flat surface 80 k and the flat surface 73 k).

The shank portion 61 of the end mill 60 is held by the taper colletchucking structure 71 by screwing the internally threaded portion 78 mon the externally threaded portion 12 m and rotating the lock nut 78 inthe fastening direction. Thus, the inward flange portion 80 presses thetaper collet 73 toward the rear end via the plane bearing 70, and thetapered surface 73 t closely fits in the tapered hole 72 of the holderbody 11, whereby the diameter of the taper collet 73 is reduced, and theshank portion 61 of the end mill 60 is held.

At this time, since the plane bearing 70 is interposed between the flatsurface 80 k and the flat surface 73 k, the frictional resistance ofboth contact surfaces that are in slide contact with each other issignificantly reduced. Thus, the pressing force resulting from fasteningthe lock nut 78 is uniformly applied to the taper collet 73.

At this time, the taper collet 73 is aligned with the axis O of theholder body 11 according to the tapered hole 72.

As a result, the end mill 60 is centered without being tilted, and isheld by the tool attaching/detaching portion 12 of the holder body 11.

A further embodiment of the present invention will be described below.FIG. 14 is an overall view showing a tool holder according to a furtherembodiment of the present invention. In FIG. 14, the upper half of thetool holder is shown by a longitudinal sectional view. In thisembodiment, the same configurations as those of the above embodimentsare denoted with the same reference characters, and description thereofis omitted. Configurations different from the above embodiments will bedescribed below.

A tool holder 40 has a side lock chucking structure 21 and a shrink-fitchucking structure 81 in the tool attaching/detaching portion 12 as astructure that chucks the shank portion 61 of the end mill 60. Theshrink-fit chucking structure 81 corresponds to a centering holding unitthat centers and holds the shank portion 61 of the end mill 60. The sidelock chucking structure 21 has a function to provide final fastening,namely a function to chuck the shank portion 61 of the end mill 60 whichhas been centered and held.

When heated to a high temperature, a tip end region of the toolattaching/detaching portion 12 thermally expands, and the innerperipheral surface 12 h thereof is increased in diameter and receivesthe shank portion 61 of the end mill 60. By subsequent cooling, the tipend region of the tool attaching/detaching portion 12 thermallycontracts, and the inner peripheral surface 12 h thereof is reduced indiameter and holds the shank portion 61. At this time, the end mill 60is aligned with the axis O of the holder body 11. As a result, the endmill 60 is centered without being tilted, and is held by the toolattaching/detaching portion 12 of the holder body 11.

A still further embodiment of the present invention will be describedbelow. FIG. 15 is an overall view showing a tool holder according to astill further embodiment of the present invention. In FIG. 15, the upperhalf of the tool holder is shown by a longitudinal sectional view. Inthis embodiment, the same configurations as those of the aboveembodiments are denoted with the same reference characters, anddescription thereof is omitted. Configurations different from the aboveembodiments will be described below.

A tool holder 50 has a side lock chucking structure 21 and a hydrochucking structure 91 in the tool attaching/detaching portion 12 as astructure that chucks the shank portion 61 of the end mill 60. The hydrochucking structure 91 corresponds to a centering holding unit thatcenters and holds the shank portion 61 of the end mill 60. The side lockchucking structure 21 has a function to provide final fastening, namelya function to chuck the shank portion 61 of the end mill 60 which hasbeen centered and held.

The hydro chucking structure 91 will be described below. Two hydraulicchambers 92, 93 are formed inside a tip end region of the toolattaching/detaching portion 12 so as to be separated from each other inthe direction of the axis O. The hydraulic chamber 92 is a ring-shapedchamber provided near the inner peripheral surface 12 h of the toolattaching/detaching portion 12 to surround the tool holding hole 122.The hydraulic chamber 93 is configured in a manner similar to that ofthe hydraulic chamber 92. The hydraulic chambers 92, 93 communicate witheach other through a communication passage 94. A hydraulic supplypassage 95 extending rearward from the hydraulic chamber 93 connects toa pressure cylinder portion 96 provided in a central portion in theaxial direction of the holder body 11. In order to facilitateunderstanding, the hydraulic supply passage 95 and the pressure cylinderportion 96 are schematically shown by broken lines.

The pressure cylinder portion 96 is a bottomed hole formed in the holderbody 11 from its outer peripheral surface. The bottom part of thepressure cylinder portion 96 is filled with hydraulic oil, and a malescrew 97 is screwed in an internally threaded portion formed in theinner peripheral surface on the opening side of the pressure cylinderportion 96. The bottom part of the pressure cylinder portion 96 issealed by a piston 98 attached to the tip end of the male screw 97.

When the male screw 97 is rotated in the fastening direction, the oilpressure in the pressure cylinder portion 96 is increased, and thehydraulic chambers 92, 93 expand radially inward in the toolattaching/detaching portion 12. Thus, the inner peripheral surface 12 his reduced in diameter near the hydraulic oil chambers 92, 93, and holdsthe shank portion 61. At this time, the end mill 60 is aligned with theaxis O of the holder body 11. As a result, the end mill 60 is centeredwithout being tilted, and is held by the tool attaching/detachingportion 12 of the holder body 11.

A yet further embodiment of the present invention will be describedbelow. FIG. 16 is an overall view showing a tool holder according to ayet further embodiment of the present invention, and shows the statewhere the tool holder of this embodiment is holding the shank portion ofthe end mill. FIG. 17 shows the state where the tool holder of thisembodiment is not holding the shank portion of the end mill. In order tofacilitate understanding, a part of the tool holder is shown by alongitudinal sectional view in FIG. 16, and the upper half of the toolholder is shown by a longitudinal sectional view in FIG. 17. In thisembodiment, the same configurations as those of the above embodimentsare denoted with the same reference characters, and description thereofis omitted. Configurations different from the above embodiments will bedescribed below.

A tool holder 100 has a side lock chucking structure 21 and a chuckingstructure 99 such as CoroGrip (registered trademark) in the toolattaching/detaching portion 12 as a structure that chucks the shankportion 61 of the end mill 60. The chucking structure 99 corresponds toa centering holding unit that centers and holds the shank portion 61 ofthe end mill 60. The side lock chucking structure 21 has a function toprovide final fastening, namely a function to chuck the shank portion 61of the end mill 60 which has been centered and held.

The chucking structure 99 will be described below. A cylindrical member110 has a tapered hole 110 h whose inner peripheral surface has the samegradient as the tip end outer peripheral surface 12 a of the toolattaching/detaching portion 12, and the cylindrical member 110 contactsthe tip end outer peripheral surface 12 a. A stopper ring 111 isattached and fixed to the tip end of the tip end outer peripheralsurface 12 a, so that the cylindrical member 110 does not come offtoward the tip end.

The inner peripheral surface of the cylindrical member 110 includes afirst annular flat surface 101, a first inner peripheral surface 103, asecond annular flat surface 102, and a second inner peripheral surface104. The first annular flat surface 101 connects to the tip end part ofthe tapered hole 110 h and faces toward the tip end. The first innerperipheral surface 103 extends further toward the tip end from the firstannular flat surface 101. The second annular flat surface 102 connectsto the rear end part of the tapered hole 110 h and faces toward the rearend. The second inner peripheral surface 104 extends further toward therear end from the second annular flat surface 102.

The first cylindrical surface 103 contacts the outer peripheral surfaceof the stopper ring 111, and a first hydraulic chamber 105 is definedbetween the first annular flat surface 101 and the stopper ring 111. Anoil passage 107 and a port 107 p, which connect to the first hydraulicchamber 105, are provided in the cylindrical member 110.

The second cylindrical surface 104 contacts the rear end outerperipheral surface 12 b of the holder body 11, and a second hydraulicchamber 106 is defined between the second annular flat surface 102 andthe annular stepped surface 12 c. An oil passage 108 and a port 108 p,which connect to the second hydraulic chamber 106, are provided in thecylindrical member 110.

In order to hold the shank portion 61 of the end mill 60 by the chuckingstructure 99, a pump is prepared, and as shown in FIG. 16, an oilpressure is supplied from the pump to the port 107 p to expand thehydraulic chamber 105. Thus, the cylindrical member 110 moves rearwardas shown by arrow in FIG. 16, whereby hydraulic fluid in the secondhydraulic chamber 106 is discharged from the port 108 p, and the taperedhole 110 h of the cylindrical member 110 closely fits on the tip endouter peripheral surface 12 a. Thus, due to the wedging action of thetapered hole 110 h and the tapered outer peripheral surface 12 a, theouter peripheral surface 12 a is strongly pressed radially inward alongits entire circumference and is reduced in diameter. As a result, thetool holding hole 122 formed in the center of the toolattaching/detaching portion 12 is also reduced in diameter, and thecylindrical portion as the front part of the shank portion 61 insertedin the tool holding hole 122 is fastened uniformly along its entirecircumference by the inner peripheral surface 12 h. Accordingly, thetool attaching/detaching portion 12 holds the outer peripheral surfaceof the shank portion 61 uniformly in the circumferential direction. Atthis time, the axis of the holder body 11 is aligned with the axis ofthe end mill 60, and the end mill 60 is held with high accuracy alongthe axis O.

As a result, the end mill 60 is centered without being tilted, and isheld by the tool attaching/detaching portion 12 of the holder body 11.

An releasing operation for releasing the shank portion 61 from thechucking structure 99 is an inverted manner from the holding operationfor holding the shank portion 61. Specifically, as shown in FIG. 17, anoil pressure is supplied from the pump to the port 108 p to expand thesecond hydraulic chamber 106. Thus, the cylindrical member 110 movesforward as shown by arrow in FIG. 17.

Although the embodiments of the present invention are described withreference to the drawings, the present invention is not limited to theillustrated embodiments. Various modifications and variations can bemade to the illustrated embodiments without departing from the spiritand scope of the present invention.

The shank structure of the end mill and the tool holder according to thepresent invention are advantageously used in machine tools.

The invention claimed is:
 1. A tool holder, comprising: a cylindricaltool attaching/detaching portion having in its center a tool holdinghole that extends from an axial tip end toward an axial rear end andthat is bounded by an inner peripheral surface of the toolattaching/detaching portion; a centering holding unit that is located inan axial tip end region of the tool attaching/detaching portion in orderto center and hold a shank portion of an end mill in a manner ofreducing a diameter of the tool attaching/detaching portion along apredetermined effective holding length from the axial tip end toward theaxial rear end of the tool attaching/detaching portion so that an entirecircumference of the inner peripheral surface of the toolattaching/detaching portion closely contacts an entire outer peripheryof a cylindrical part of the shank portion along its entirecircumference, wherein the cylindrical part has a circular cross sectionwith a constant radius along a predetermined axial dimension of theshank portion, and the cylindrical part is located closer to the axialtip end than an axial rear end part of the shank portion inserted in thetool holding hole; a side lock chucking structure comprising: aplurality of side lock bolts including first and second side lock boltsthat are respectively screwed in first and second through holes whichare formed at different circumferential positions in the axial rear endpart of the tool attaching/detaching portion, wherein the first throughhole is provided at a position of a predetermined angle in a range from60 to 120 degrees, both inclusive, about an axis of the toolattaching/detaching portion with respect to the second through hole, andthe first and second through holes extend from an outer peripheralsurface of the tool attaching/detaching portion to the inner peripheralsurface thereof that bounds the tool holding hole, wherein the first andsecond through holes are tilted at a predetermined angle in a range from1 to 10 degrees, both inclusive, with respect to a directionperpendicular to an axis of the tool attaching/detaching portion so thatradially outer peripheral ends of the first and second through holes arecloser to the axial tip end of the tool attaching/detaching portion thanradially inner peripheral ends of the first and second through holes,wherein the first and second side lock bolts are screwed so that flattip end faces formed at tip ends of the first and second side lock boltsabut on first and second tilted flat surfaces formed on an outerperipheral surface of an axial rear end part of the shank portion of theend mill on the condition that the cylindrical part has been centeredand held by the centering holding unit; and a stopper member provided ona bottom side of the tool holding hole and adapted to define an axialposition of the shank portion of the end mill inserted in the toolholding hole; wherein the tool holder is configured to chuck the shankportion of the end mill by the centering holding unit and the side lockchucking structure.
 2. The tool holder according to claim 1, wherein thecentering holding unit includes a taper that is formed in the outerperipheral surface of the tool attaching/detaching portion so as to betapered toward the axial tip end, a cylindrical fastening member thathas an inner peripheral surface tapered at a same angle as the outerperipheral surface of the tool attaching/detaching portion and surroundsthe outer peripheral surface of the tool attaching/detaching portionwhich is located closer to the axial tip end than the side lock bolts, aplurality of needle rollers that are placed in an annular space betweenthe inner peripheral surface of the fastening member and the outerperipheral surface of the tool attaching/detaching portion, and aretainer that holds the needle rollers so that the needle rollers aretilted at a predetermined angle in a circumferential direction withrespect to an axis of the tool attaching/detaching portion, and thefastening member is rotated so that the needle rollers revolve in ahelical pattern while rotating, whereby the tool holding hole is reducedin diameter or is restored.
 3. The tool holder according to claim 1,wherein each respective one of the side lock bolts includes a bolt bodythat is screwed in a respective one of the through holes, and a pressingmember having a pressing surface as a respective one of said flat tipend faces that abuts on a respective one of the tilted flat surfacesformed on the shank portion of the end mill, and being attached to therespective tip end of the bolt body so that orientation of the pressingsurface can be changed as desired.
 4. The tool holder according to claim1, wherein the respective flat tip end face of each respective one ofthe side lock bolts is surface-treated so as to have a higher frictioncoefficient compared to a condition thereof without beingsurface-treated.
 5. The tool holder according to claim 1, wherein: thestopper member has a communication passage extending through the stoppermember in the axial direction, and an opening at a tip end of thecommunication passage is configured to connect to an opening at a rearend of a fluid passage of the shank portion of the end mill.
 6. The toolholder according to claim 1, wherein the plurality of side lock boltsconsists of only a total of two of said side lock bolts being said firstand second side lock bolts, and said tool holder includes no side lockbolts other than said first and second side lock bolts.
 7. The toolholder according to claim 1, wherein each one of said side lock bolts islocated diametrically opposite a solid inner wall portion of the innerperipheral surface of the tool attaching/detaching portion in the toolholding hole thereof.
 8. The tool holder according to claim 1, whereinthe side lock bolts are arranged circumferentially asymmetrically arounda circumference of the tool attaching/detaching portion.
 9. The toolholder according to claim 8, wherein a circumferential portion in arange from 240 to 300 degrees of the circumference of the toolattaching/detaching portion has none of the side lock bolts arrangedtherein.
 10. The tool holder according to claim 1, further comprising amount portion at said axial rear end of said tool holder, and a flangeportion axially between said mount portion and said toolattaching/detaching portion, wherein said tool attaching/detachingportion includes a rear end portion axially between said flange portionand said centering holding unit, and wherein said side lock chuckingstructure including said side lock bolts in said through holes isprovided in said rear end portion axially between said flange portionand said centering holding unit.
 11. The tool holder according to claim10, wherein the tool holding hole has a constant diameter from the axialtip end to and including the rear end portion at which the through holesand the side lock bolts are provided.
 12. The tool holder according toclaim 1, wherein the tool holding hole has a constant diameter from theaxial tip end to and past the through holes and the side lock bolts. 13.The tool holder according to claim 1, wherein the tool holding hole hasthe same diameter in the axial tip end region and at an axial locationaxially between the stopper member and the side lock bolts.